AGC has developed a process simulation–based digital twin that reproduces the actual operation of a plant in real time. Get a detailed overview of the digital twin of a VCM plant, its objectives, how AVEVA™ PI System™ was used, and the subsequent results. The digital twin combines first-principles models with statistical models to provide unprecedented process monitoring and operational optimization. To build it, we used AVEVA PI system (1) as an infrastructure, (2) as a user interface, and (3) as a tool to connect the last mile. The process digital twin has great potential not only for process monitoring and process insight, but also for operational optimization. In addition, the AVEVA PI System has proven to be an indispensable tool for building and using process digital twins.